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Early leaf spot of groundnut (Cercospora arachidicola) Photo: Swarochi Tathagath · CC BY 4.0 · source ↗

Early leaf spot of groundnut (Cercospora arachidicola)

Early leaf spot (ELS) is caused by Cercospora arachidicola Hori (anamorph; teleomorph Mycosphaerella arachidis). It is one half of the tikka leaf-spot complex of groundnut, the other being late leaf spot. ELS is the first foliar disease to appear in the season — typically 30-35 days after sowing — and on its own can cause 15-25 percent pod yield loss in susceptible cultivars.

Identification

Lesions appear first on lower leaves as small chlorotic flecks that enlarge into circular to sub-circular spots 1-10 mm in diameter. Mature lesions are reddish-brown to dark brown on the upper leaf surface and lighter brown below, typically with a distinct yellow halo — this halo is the key feature separating ELS from late leaf spot (which lacks a halo and is darker below). Severe infection causes premature defoliation; pegs and pods can also bear lesions.

Hosts and lifecycle

C. arachidicola is specific to cultivated groundnut and a few wild Arachis species. The fungus over-seasons on infected debris and volunteer plants; conidia are produced on conidiophores arising from stromata in old lesions. Conidia are dispersed by wind, rain splash and insects. Infection requires 5-10 hours of leaf wetness at 20-26 deg C; the latent period is 10-14 days, shorter than late leaf spot.

Damage and economic impact

ELS arrives early and predisposes the canopy by reducing photosynthetic area before pod fill. Where the seasonal sequence is ELS-then-LLS-then-rust (the usual Anantapur kharif pattern), the early infection seeds inoculum for the later epidemics. Yield loss attributable to ELS alone is typically 15-25 percent but rises sharply when fungicide protection is delayed past 35-40 DAS.

Management

  • Resistant varieties: ICGV 86699, ICGV 87165, ICGV 87187 and breeding lines derived from Arachis cardenasii show useful field resistance; Kadiri-9 has moderate field tolerance under Anantapur conditions.
  • Cultural: deep summer ploughing; clean-cultivation of volunteer plants; crop rotation with non-host cereals; avoid late sowing.
  • Chemical: prophylactic mancozeb 75 WP at 2 g/L or chlorothalonil 75 WP at 2 g/L starting 30 DAS, repeated at 15-day intervals. For curative action use carbendazim 50 WP at 1 g/L or systemic triazoles (tebuconazole, propiconazole, hexaconazole) at 1 ml/L. ICAR-DGR's recommended sequence is mancozeb -> tebuconazole + trifloxystrobin -> mancozeb across three sprays at 30, 45 and 60 DAS.

Because ELS, late leaf spot and rust share weather windows, in practice farmers manage all three through the same spray schedule rather than targeting ELS in isolation.

See also: Tikka leaf spot in groundnut, Late leaf spot, Groundnut rust, Groundnut crop.

Sources

  1. Early and late leaf spots of groundnut. ICAR-Directorate of Groundnut Research, Junagadh.
  2. Cercospora arachidicola factsheet. CABI Plantwise.
  3. Foliar fungal diseases of groundnut. ICRISAT, Patancheru.